Programmed braking for elevators and the like

ABSTRACT

An elevator includes a motor for accelerating a cab and a brake for decelerating it, the two being operated during mutually exclusive time intervals. The brake mechanism is biased to brake the cab and has an electrical winding to defeat the biasing spring. An amplifier is connected by means of a selector switch to control energization of the motor during acceleration and of the brake winding during deceleration. The input to the amplifier comes from a summing network which develops the difference between two control signals. One of the control signals comes from a tachometer generator and is proportional to the speed of the elevator car, while the other control signal comes from a brake program device or an acceleration program device. The program devices are designed to provide braking and acceleration programs respectively which are functions of the distance of the elevator car from a particular floor. During deceleration the braking effort is smooth and continuous right up to the moment of dead stop.

United States Patent 72] Inventor Raffaello Vlzzotto 3,250,975 5/1966Pepper 318/229 o 21 A l N Primary Examiner-Gris L. Rader 0a.: 1969Assistant Examiner-W. E. Duncanson, Jr. Pafemed 1971Attorney-HubbelLCohen&Stiefel 9 a [73] Assignee G. Falcon: C.S.p.A.

Nova'raJtaly gg ';g :2 m ABSTRACT: An elevator includes a motor foraccelerating a p cab and a brake for decelerating it, the two beingoperated during mutually exclusive time intervals. The brake mechanismis biased to brake the cab and has an electrical [54] PROGRAMME) BRAKINGFOR ELEVATORS AND winding to defeat the biasing spring. An amplifier isconnected b means of a selector switch to control energization of theTHE LIKE y 20 Claims, 11 Drawing Figs motor during acceleration and ofthe brake winding during deceleration. The input to the amplifier comesfrom a 187/29 R summing network which develops the difference betweentwo 1 f B6611/32 control signals. One of the control signals comes froma tachometgr generator and is proportional to the speed of [he318/229,363,369,372, 143 elevator car, while the other control signalcomes from a brake program device or an acceleration program device. The[56] References cued program devices are designed to provide braking andac- UNlTED STATES PATENTS celeration programs respectively which arefunctions of the 2,403,125 7/1946 Santiniet al. 187/29 distance of theelevator car from a particular floor. During 2,746,567 5/1956 Guttingeret al... 187/29 deceleration the braking effort is smooth and continuousright 3,155,891 11/1964 Rosa 318/143 up to the moment ofdead stop.

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PROGRAMMED BRAKING FOR ELEVATORS AND THE LIKE CROSS-REFERENCES Thisapplication is a continuation-in-part of my earlier application Ser. No.582,871 filed Sept. 29, 1966, entitled Apparatus for Controlling Liftsand the Like."

FIELD OF THE INVENTION The present invention relates to apparatus forthe control of lifting equipment such as elevators, cable cars,funicular railways, conveyors and the like. It is primarily concernedwith programmed braking of such equipment.

THE PRIOR ART Elevators and other types of lifting equipment arecommonly driven by an electric motor. Means are provided in the elevatorshaft for sensing the position of the elevator cab relative to a floorof the building, and the energization applied to the electric motor isincreased as a function of cab displacement so as to obtain gradualacceleration when leaving that floor. Braking apparatus is also providedwhich acts on the mechanical transmission between the motor and cab todecelerate the cab when it reaches its destination. The brake mechanismis electrically controlled according to a predetermined program as afunction of the approach of the elevator cab to its destination floor.

The principal object of such programmed braking is to provide a gradualand therefore pleasant stop for the occupants of the elevator cab, freeof jolts. Another important object of programmed braking is to stop theelevator cab on a level with the destination floor. Prior art programmedbraking systems, however, are inadequate in these and other respects.

One type of system which has been used for the gradual stopping ofelevator equipment employs a large flywheel on the shaft of a singlespeed elevator drive motor. In such a system the flywheel helps tosmooth the acceleration and deceleration of the cab, but it is not asatisfactory solution. Current consumption consequent heating of themotor windings are excessive when accelerating the large flywheel mass,and conversely the brake linings suffer extensive wear and heating upondeceleration.

Some improvement is obtained by using a two-speed motor in conjunctionwith a heavy flywheel, particularly a motor of the type which can beswitched from a relatively small number of poles to a relatively largenumber. In that type of system the higher speed of the motor serves foracceleration and constant speed operation, while the lower speed is usedfor braking. But even with a two-speed motor, the flywheel must still berelatively large in order to provide gradual speed transitions and anadequate degree of precision in stopping the cab at floor level. Thus,the problems associated with the use of a massive flywheel are notentirely avoided by the use of a two-speed motor. Specifically, theproblem of brake lining wear is reduced because of the brakingcontributed by the motor; but the problem of motor heating remainsbecause of the need to accelerate the massive flywheel, and is evenincreased because motor braking heats the motor windings during thedeceleration phase. Moreover, such systems have sharp speed transitionswhich are detectable by the passengers; and the slow coasting intervalswhich follow the transitions consume an in ordinate amount of time foreach stop, inconveniencing the passengers and lowering the serviceefficiency. Under conditions of high demand, this is a serious drawback.

Further improvement has been obtained by employing a prior art system ofthe type seen in US. Pat. No. 2,746,567 of Guttinger, which determinesthe difference in voltage between a signal representing the actualinstantaneous speed of the elevator, and another signal that varies in amanner representing the desired elevator speed as a function of itsinstantaneous displacement from the destination level. This differencevoltage is then used to control the instantaneous braking force duringan initial phase of deceleration; but during the latter stages ofdeceleration the Guttinger system abandons any attempt at proportionalcontrol as a function of actual speed, and instead allows the elevatorto coast at a predetermined and constant speed regardless of variableconditions. Thus, like the two-speed motor approach, the Guttingersystem also has two distinct deceleration phases, with a discerniblespeed transition between them; and suffers from the time-consuminginefficiency of a slow coasting intervaLMoreover, in order to vary thebrake program signal as a function of displacement, Guttinger employs aslide wire potentiometer. Such a device can not easily be adapted to asystem requiring a nonlinear relationship between voltage anddisplacement. Yet such a relationship is needed for a sophisticatedbrake program which maximizes passenger comfort.

SUMMARY AND OBJECTS OF THE INVENTION The principal objective of thisinvention is to achieve smooth elevator braking and precise stopping.Another object is to provide a comfortable, jolt-free andtransition-free ride for elevator passengers, particularly during thedeceleration phase. Still another object is to stop the elevatorprecisely on a level with the destination floor each time, withoutregard to variations of elevator load. It is also an object to avoidservice slowdowns and achieve a level of efficiency which is adequatefor peak demand periods. A subsidiary object of the invention is to takefurther advantage of the apparatus which achieves this improvement inbraking performance to aid also in the gradual acceleration of theelevator cab.

In order to achieve these objectives, apparatus in accordance with thisinvention includes means for producing an electric signal proportionalto the speed of the elevator, preprogrammed signal producing means,variable force braking means, and a control circuit for the brake means.Throughout the entire deceleration of the elevator, the control circuitproduces a signal which is a function of the difference between thesignal from the preprogrammed means and the speed-proportional signal,and supplies this difference signal to the brake means for varying thebrake force in accordance therewith.

The apparatus thus briefly summarized has the advantage that the brakingforce is applied continuously (although diminishing proportionately)right up to dead stop. This eliminates the sense of discontinuity whichthe passengers experience when multiphase braking apparatus shifts fromone phase to the succeeding phase. Moreover, a special nonlinear brakeprogram can be employed to maximize passenger comfort. In addition, thistype of system adjusts the braking force as a function of the differencebetween the instantaneous speed of the elevator cab and the programmedspeed called for at that moment, rather than as a function of thedistance from the destination floor. The result is precise andrepeatable stopping of the elevator cab on a level with the destinationfloor regardless of variable elevator load conditions. The system isalso faster, more efficient, and more economical in several respects.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic circuit diagramof an elevator braking and starting program control circuit inaccordance with this invention;

FIG. 2 is a schematic illustration of an elevator car and a verticalshaft in which the car moves, with position sensing means mounted on thewalls of the shaft for use with the program control circuit of FIG. 1;

FIG. 3 is a schematic circuit diagram of position sensing switches usedwith the means of FIG. 2;

FIG. 4 is a schematic illustration of an alternative set of positionsensing switches for use with this invention;

FIG. 5 is a schematic diagram of a circuit employing position sensingswitches of the kind illustrated in FIG. 4;

FIG. 6 is a sectional view, partly schematic in nature, showing detailsof a typical position sensing switch of the kind in FIGS. 4 and 5;

FIG. 7 is a schematic illustration of the sensing switch of FIG. 6 inconjunction with an activating element which is mounted on the elevatorcab;

FIG. 8 is a graph of elevator cab velocity versus displacement comparingthe performance of a prior art system, using a single speed motor, withthat of the present'invention under varying elevator load conditions;

. FIG. 9 is a similar graph of elevator cab velocity versus displacementcomparingthe performance of another prior art" system, using a two-speedmotor, with that of the present invention under varying conditions ofelevator load;

FIG. 10 is a diagram of elevator cab velocity versus time for a priorart system of the two-speed motor type; and

FIG. 11 is a diagram comparable to FIG. 10 but showing the performanceof the system of this invention.

The same reference characters refer to the same elements throughout theseveral views of the drawing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 provides anoverall view of the elevator control system of this invention, in whicha conventional single speed three-phase electric motor 4 is mechanicallyconnected to drive a brake drum 5 and an elevator drive pulley 3.Suspended from the drive pulley are an elevator cab l and itscounterweight 2.

The motor 4 has reaction windings 19, 20 and 21 which are in seriesrespectively with three phases of the motor drive windings, and areenergized under control of a switch 38. When the switch 38 is closed inonedirection the motor 4 lifts the elevator cab 1, and when the switchis closed in the other direction the motor lowers the elevator cab. Thereaction windings are wound on saturable cores (not shown) controlled byrespective magnetizing windings 19, 20 and 21 of a motor speed controlmagnetic amplifier circuit 11. A lead 15 is connected in series with themagnetizing windings 19, 20' and 21 to apply a speed control signal tothe circuit 11. This series connection imposes a voltage drop upon thethreephase system, but this is not excessive under the power consumptionconditions likely to occur in an elevator system of this kind.

The brake drum 5 is acted upon by a brake 6 in response to the urging ofa biasing spring 7. The arrangement is a fail-safe one, in that thespring 7 normally causes the brake to act upon the drum, and thusprevent a precipitous drop of the elevator cab 1. Operation of the brake6 is defeated only when the spring 7 is positively overcome byenergizing a brake defeat winding 8 which raises the brake 6 against theurging of the spring 7. Thus it is apparent that the brake 6 willoperate when the system is totally disabled and the brake defeat winding8 cannot be energized.

The elevator system further includes an acceleration program circuit 23and a brake program circuit 30 which are designed to provide gradualstarting and stopping respectively, so as to minimize passengerdiscomfort. An additional purpose of the brake program circuit 30 is toreduce the elevator cab speed prior to dead stop, so that the cab canthen be halted accurately on a level with the destination floor.

The program circuits 23 and 30 are combinations of switches mounted uponthe elevator and actuated at proportionate distances from the variousfloors during the passage of the elevator cab 1 in order to sense theposition of the cab relative to a floor. These circuits also comprisevarious additional components connected to the position detectingswitches to provide programmed control signals on leads and 31 whichcontrol the speed of the motor 4 and the decelerating force of the brakemechanism 6 respectively. In order to accomplish this, the voltage onthe lead 25 controls the speed control signal applied over lead 15 tocircuit 11, and

the voltage on lead 31 controls the energization of the brake defeatwinding 8.

In accordance with this invention, a tachometer generator 24 rotateswith the mechanical transmission of the elevator and produces a voltageoutput which is proportional to the speed thereof. This voltage is thenapplied to one input of a difi'erence network 33. The other input to thedifference network arrives over a lead 29 which can be connected eitherto lead 31 to receive the output of the brake program circuit 30, or tolead 25 to receive the output of the start program circuit 23. Theselection between these two leads is made by means of a switch 37including three ganged sections 35, 28 and 14. Switch section 28 has anarm 26 which can be moved between contacts 32 and 27 to connect lead 29to leads 31 or 25 as required.

The plus and minus signals at the two inputs to the difference network33 do not necessarily indicate the absolute polarity of these inputs,but rather indicate that these inputs are subtracted within the networkso that the resulting output applied to terminal 22 of an amplifier 9 isa signal representing the difference between the actual speed of theelevator cab 1 as the desired speeds of the elevator cab, rather than ofmere distance from the destination floor without regard to speed. Thedesired speed called for by the brake program circuit 30 is, of course,a function of the distance of the elevator cab from the destinationfloor, as in the past. But the desired speed is related to the actualspeed of the cab by the difference network 33 to develop the signalwhich actually controls braking. Moreover, the brake winding 8 remainsunder control of the variable signal provided by program circuit 30during the entire deceleration.

The result is that the braking force is not divided up into distinctphases. Nor is it required to be fully on or fully off. Instead, theforce exerted at all times is proportional to the instantaneousdifference between the actual and desired elevator cab speeds.Consequently it varies smoothly, and continues over the entiredeceleration interval without sudden transitions as in a multiphasebraking program. Indeed the braking effort continues right through tothe moment of dead stop.

In FIG. 8 the solid line graphs depict the velocity V of the elevatorcab as a function of its displacement S when the cab is traveling upwardtoward a destination floor, and is decelerated according to thisinvention. Curve b represents a condition of positive load (cab plusload heavier than counterweight), while curve 2 represents a conditionof negative load (cab plus load lighter than counterweight). Arepresents the point at which deceleration begins. P represents thedestination floor. It is seen that the solid line curves representingdeceleration in accordance with this invention converge exactly to pointP; i.e. they both stop precisely level with the destination floor Pdespite the difference in load conditions.

For the purpose of comparison, the dashed line curves of FIG. 8represent deceleration by means of a single speed motor and flywheelsystem according to the prior art. Once again curve b is for positiveand curve a for negative load con- 'ditions.

The difference between these load conditions causes the prior art curvesto diverge to points P1 and P2 below and above the destination floorrespectively. Thus it is apparent that the system of this invention is agreat improvement in terms of precise and repeatable stopping.

FIG. 9 is a similar diagram comparing the present results with thoseachieved using a two-speed motor system. Once again the solid linecurves represent the system of this inven-' tion for conditions ofpositive load (curve b) and negative load (curve a), and an upwarddirection of cab. The deceleration program according to this inventionstarts at location B, and once again the curves converge smoothly to adead stop at the destination floor P. In contrast, the dashed linecurves, b

representing positive load conditions and a representing negative loadconditions, show the inferior results achieved by the prior art.

The prior art braking program must begin at a more distant location B.Then the dashed line curves undergo a fairly sharp transition to aconstant speed coasting interval terminating at location A. This isfollowed by another fairly sharp transition to a final braking interval.The latter is not efi'ective in most cases to stop the elevator cabprecisely at the destination floor P. Instead, the negative load curveterminates at a location P4, i.e. the elevator coasts upwardly to a stopsomewhat above the level of the destination fioor; while the positiveload curve terminates at a location P3, stopping short in its upwardtravel at a point somewhat below the level of the destination floor.

Since the prior art braking program begins at a more remote location B,and since a low speed coast is required, time is consumed in bringingthe elevator cab to a stop. This is clearly illustrated by thecomparison between FIGS. and 11. FIG. 10 is a graph of cab velocity Vversus time t for a prior art braking program of the multiphase type.The total time interval depicted in the graph covers a complete elevatortrip, and is divided into three segments. These include a startinginterval during which the velocity increases, followed by an interval oftravel at a constant maximum velocity. Then there is an interval ofbraking which itself is divided into three phases. The first two phases,which together make up the programmed braking sequence, include aninterval of maximum braking force during which the cab velocitydeclines, followed by an abrupt transition to an extended coastinginterval of travel at a nearly constant low speed until the cab reachespoint a. Then there is another sharp transition to a second interval ofmaximum braking which finally brings the cab to a dead stop at point b.

For comparison purposes, FIG. 11 shows the corresponding curve for anelevator in accordance with the present invention. Once again the tripstarts with an acceleration interval (which can be programmed or not),followed by a travel interval of constant, maximum speed and an intervalof programmed braking. Here again we see that the brake continueswithout sharp transitions right down to dead stop. But note also thatthe trip ends in a much shorter time than the one illustrated in FIG.10, as shown clearly by the time lost" interval.

The graph of FIG. 11 also reveals that with the system of this inventionthe motor is off during the programmed braking interval. This is incontrast to the prior art elevator trip of FIG. 10 in which the motor ison, either for acceleration or for braking, throughout the trip,generating heat all that time. In the present system braking can be leftentirely to the braking mechanism 6.

Brake mechanism 6 is adequate because a massive flywheel is no longernecessary to smooth the phase transition of the prior art. With a largeflywheel, electrodynamic braking by the motor would be necessary toarrest the rotating mass.

In the present system a small flywheel can be used, the sole function ofwhich is to provide enough inertia in the system to make certain thatthe cab will arrive at the destination floor even under the worst loadconditions. Such a flywheel is much less massive than the type requiredby prior art elevator control systems.

For a more detailed understanding of the brake program circuit 30, werefer to FIG. 2 showing an elevator shaft C in which the cab 1 rides.The shaft is divided into distinct floor segments by the horizontaldashed lines. Within each floor area are switch activating means M and Nsecured to the wall of the shaft. These are designed to actuate switchesG, which are secured to the elevator cab l and are divided into a firstgroup of switches G1 actuated by devices M, and a second group G2 whichare actuated by devices N, at each of the floors. At the instantdepicted in FIG. 2, the elevator cab l is at floor P and the devices M,and N are positioned adjacent switch groups G1 and G2 respectively. Thedevices M and N at each floor are vertically offset from each other insuch manner that one of them activates its associated group of switchesduring upward movement of the elevator cab 1, while the other activatesits associated group of switches during downward movement of theelevator cab.

For a close look at one particular embodiment of a switch and actuatormechanism of the type generally illustrated in FIG. 2, we turn to FIG. 3which shows a group of switches Cl through C4 mounted upon the elevatorcab and cooperating with a switch actuator device Tl during upward cabmotion. A similar series of switches is mounted upon the cab at therighthand side of FIG. 3, and cooperates with an actuating device T2during downward motion. The switch actuator devices TI and T2 are bothmounted on a central vertical rail O which runs through the elevatorshaft. Since the switches C1 through C4 and their counterparts at theright-hand side of FIG. 3 are mounted upon the elevator cab, they moverelative to their respective fixed actuating devices T1 and T2.

Resistors Rl through R5 are connected to a power source terminal I and'to the switches Cl through C4 as shown in the circuit of FIG. 3, whilea similar network of resistors is similarly connected to the switches atthe right-hand side of FIG. 3. As each switch plunger contacts theactuator device T1 or T2 thereof, it is driven from a positionillustrated by switches Cl and C2 to the position illustrated byswitches C3 and C4.

When none of the switches Cl through C4 are activated by the slide T1,the power source terminal I is directly connected over a low impedancepath to a switch Kl. This switch, which is closed during upward elevatorcab travel, is connected to ground through an RC network comprisingresistors R10 and R20 and capacitor C0. An output voltage is picked offacross the capacitor and connected to a terminal U which represents theoutput terminal of the brake program circuit 30 of FIG. I.

As the elevator cab travels upward toward its destination floor,switches C1 through C4 are closed in that order. When switch C1 isclosed, resistor R1 is connected in series between terminal I and the RCnetwork. Next, when switch C2 is closed resistors R1 and R2 are bothconnected in series between terminal l and the RC network, and similarlyfor the remaining switches and resistors. In other words, as eachsucceeding switch Cl through C4 is closed, an additional one of theresistors R1 through R4 is cumulatively added in series between terminalI and the RC network. Even though switches Cl through C4 which werepreviously actuated are later allowed to reopen by the continuing motionof the elevator cab, the resistors remain in circuit. As a result, thevoltage impressed upon the RC network decreases in four discrete steps.However, the integrating action of the RC network smooths these steptransitions to provide a gradually decreasing brake program outputvoltage at terminal U. Consequently, as the elevator cab rises towardits destination floor the brake program control voltage issued bycircuit 30 decreases smoothly to call for declining elevator cab speedlevels. The desired speed called for is thus a function of thedisplacement of the cab from the destination floor; and remains so allthe way to the dead stop at floor level. There is no transition to aconstant coasting speed (which would not be a function of displacement).

The switches and the resistors at the right-hand side of FIG. 3 operatein the same manner for downward decelerating motion of the elevator cab,as it approaches its destination floor from above. Under thosecircumstances the switch K2 is closed to connect the right-hand side ofthe circuit to the RC network. I

In order to avoid a condition in which all the switches are open for aninstant during the passage from switch to switch, the vertical dimensionof the actuators T1 and T2 exceeds the maximum distance between theoperating plunger of any two adjacent switches actuated thereby. Thus,for example, slide Tl will close switch C2 before releasing switch C1,to avoid undesirable discontinuities in the voltage applied to the RCnetwork.

There is no departure from the programming of brake force as a functionof displacement until final stopping and holding of the elevator cab,which occurs only when the cab reaches the destination floor and opensthe switch 18 of FIG. I to cut off the brake defeat winding 8 entirely.Thus it is seen that the braking force is continuously exerted andsmoothly varied selected to determine the braking program. For example,so

far as upward travel is concerned, the distance between adjacentswitches gradually decreases from switch C1 to switch C4. If the valuesof the resistors R1 through R4 are the same, and if the distance betweenadjacent switches decreases parabolically as a function of the distanceto the destination floor so as to match the decrease in cab speed underdeceleration, then the time interval between the activation of any twosuccessive switches Cl through C4 is constant, and the deceleratingforce exerted by the brake mechanism is constant. This arrangementproduces maximum passenger comfort as well as obtaining the bestsmoothing results from the RC integrating network. The same is true forthe upward mo tion circuit depicted at the right-hand side of FIG. 3. Itis evident that a nonlinear (i.e. parabolic) control function such asthis would be very difficult to achieve if a slide wire potentiometerwere used in place of i the discrete switches C1 through C4, etc. v

The switch arrangement of FIG. 4 and its associated circuit of FIG. 5 issimilar in most respects to that of FIG. 3, except that there isemployed a type of switch illustrated in FIG. 6. This includes a pair ofmagnetically actuated reed type contacts 61 enclosed within a glassenvelope 62. A casing 64 of a material which is nonpermeable surroundsthe envelope 62. A permanent magnet 63 is assembled with the casing 64,leaving a space therebetween which can be traversed by a soft iron plate70 as seen in FIG. 7. Normally the magnet 63 closes the contacts 61, butwhen the iron plate 70 intervenes, it acts as a flux shield and allowsthe contacts 61 to open.

As seen in FIG. 4, a group of such switches 41 through 45 are mountedupon the elevator cab and move therewith to traverse a soft iron switchactuating shield 40 which is mounted upon a support 46 secured in placeupon the vertical rail 47 within the elevator shaft. Switches 41 through45 are actuated sequentially by the shield 40 as the elevator cab movesupwardly within the shaft, and serve a function similar to that ofswitches Cl through C4 of FIG. 3. A similar arrangement of switches isseen at the right-hand side of FIG. 4, and serves for downward cabmovement.

FIG. 5 shows the electrical connection of switches 41 through 44 to anetwork of resistors 57, 58, 59, etc. which are similar in purpose tothe resistors R1 through R4 of FIG. 3. There is also an RC integratingnetwork comprising resistors 54 and 55 and a capacitor 56. The negativeterminal of the network is designated 50, the output terminal at whichthe brake program signal voltage appears is designated 51, and a circuitpoint at the end of the string of resistors is grounded.

In this circuit those switches with single prime reference numerals areemployed for upward motion of the elevator cab, and are connected to aswitch 52 which closes in response to such motion. The switches withdouble prime reference numerals correspond to those at the right-handside of FIG. 4, in that they are employed for downward elevator cabmotion and are connected to a switch 53 which closes during such motion.The diodes D1 through D4 and D1 through D4 etc. are employed to preventsneak circuits between switches 41 through 44' and switches 41" through44".

When all the switches 41 through 44 in the group which is currentlyoperative are closed, then all the resistors are out of the circuit. Asswitch 41' is closed first during upward cab motion or switch 41" isclosed first during downward elevator cab motion, resistor 57 isinsertedinto the circuit. As subsequent switches in the string are closed innumerical order as a result of continuing motion of the elevator cab,additional resistors 58, 59 etc. are inserted into the circuit in seriescumulatively, i.e. in addition to those resistors previously inserted inthe circuit. The result is a brake program output voltage at terminal 51which decreases in the manner discussed above, Note that the diodes inFIG. 5 make it possible to use only a single string of resistors insteadof a double string as in FIG. 3.

With any of the brake program circuit embodiments discussed herein, theresult is a continuously declining brake program voltage issuing fromcircuit 30 of FIG. 1 and applied over lead 31, switch section 28, andlead 20 to the input of the difference network 33. This causes thedifference signal applied to the amplifier input 22 to be regulated inaccordance with the brake program circuit, but with reference to theactual speed of the elevator cab l, as measured by the tachometergenerator 24. The result is a smooth and continuous application ofbraking force over the entire deceleration interval, right up to theopening of switch 18 when the elevator cab reaches its destination floorand makes a dead stop precisely at floor level.

Although the invention is concerned primarily with programmed braking,an additional advantage of the invention is that the difference network33 and amplifier 9 can also be used during acceleration under control ofthe program circuit 23 to provide programmed starting.

Other advantages of the invention are that, with the reduction offlywheel, there is a corresponding reduction in the torque required foraccelerau'ng, and therefore power consumption during starts is reduced.This is economical not only from the standpoint of the continuing costof electrical energy, but also permits a less expensive motor to beused, allowing a saving in initial cost. In addition the lower flywheelmass means that less kinetic energy must be dissipated upon braking, sothat there is less wear on the brake linings and less heat developed.The absence of a heavy flywheel also means that under emergencyconditions the brake mechanism is better able to bring the elevator to asudden stop because there is less mass to deeelerate.

Of course, fail-safe braking is maintained, in that even a total failureof the electrical control system would have no greater consequences thana deenergization of the brake defeat winding, resulting in maximumbraking force under spring bias, so that the elevator cab would bebrought to a safe halt.

The programmed starting feature which is an additional advantage of theinvention makes possible additional power economies, and a reduction inthe heating of the motor drive windings, during the acceleration phase.Finally, it may be observed again that the system of this inventionsaves valuable time by shortening the programmed stopping time veryconsiderably, and does so without jarring the passengers. On thecontrary, there is a marked improvement in the smoothness of thedeceleration surge. Furthermore, the passengers are assured of aperfectly level stop at the destination floor when the elevator comes toa halt, which is at least a convenience to the passengers and may evensave them from tripping and falling when they emerge from the cab.

What is claimed is:

l. Elevator apparatus for performing a transitionless elevator brakingprogram, said apparatus comprising:

an elevator,

an electric motor for powering said elevator,

a destination floor,

means for producing an electric signal proportional to the speed of saidelevator,

preprogrammed means for producing a signal which is a continuousfunction of the displacement of said elevator from said destinationfloor without interruption until its arrival at said destination floor,

variable force brake means,

and control circuit means for said brake means, said control circuitmeans including difference means for producing a signal which is afunction of the difference between the signal produced by saidpreprogrammed means and said speed-proportional signal, and means forsupplying said difierence signal to said brake means for varying thebrake force in accordance with said difference signal withoutinterruption until the arrival and stop of said elevator at saiddestination floor, whereby said transitionless elevator braking programis provided until said arrival and stop.

2. Elevator apparatus according to claim 1, wherein said variable forcebrake means includes an electromagnetic winding for reducing brakingforce as excitation thereof is increased, and said means for supplyingsaid difference signal to said brake means is continuously connected tosaid winding until the arrival of said elevator at said destinationfloor.

3. Elevator apparatus as in claim 2, further comprising means fordisconnecting said brake control circuit means from said winding whensaid elevator arrives at said destination floor.

4. Elevator apparatus according to claim 2, further comprising switchingmeans for deenergizing said electric motor whenever said brake controlcircuit means is in operation.

5. Elevator apparatus as in claim 4, further comprising means formaximally energizing said winding to reduce said brake force to aminimum whenever said electric motor is energized.

6. Elevator apparatus according to claim 2, wherein said variable brakemeans includes a brake drum and a member operatively engageabletherewith for exerting a braking torque thereon, means for biasing saidmember toward said drum to exert maximum torque thereon, saidelectromagnetic winding being in operative relation with said member forexerting a torque reducing force on said member which varies as afunction of said difference signal.

7. Elevator apparatus according to claim 6, wherein said biasing meanscomprises a spring.

8. Elevator apparatus according to claim 2, wherein said preprogrammedmeans comprises a voltage source, a plurality of impedances; anddiscrete switching means located at spaced locations whereby to beresponsive to the distance between a preselected point on said elevatorand a preselected stationary point for selectively connecting saidimpedances across said voltage source in discrete steps for varying theoutput signal produced thereby as a function of the spacing between saidswitch locations and of the travel of said eleva- I01.

9. Elevator apparatus as in claim 8, further comprising integratingmeans for smoothing said discrete switching transitions to provide asmooth output from said preprogrammed means.

10. Elevator apparatus according to claim 8, wherein consecutivespacings between said switch locations are related nonlinearly.

11. Elevator apparatus according to claim 8, wherein said switchingmeans comprises two groups of switches, one of said groups for upwardelevator movement and the other of said groups for downward elevatormovement, and said plurality of impedances comprise two groups of seriesconnected resistors for connection across said voltage source, one ofsaid resistor groups for connection during upward elevator movement andthe other of said resistor groups for connection during downwardelevator movement, said one group of switches for selectively connectingthe resistors from said one group into and out of circuit across saidvoltage source; and said other group of switches for selectivelyconnecting the resistors from said other group into and out of circuitacross said voltage source.

12. Elevator apparatus according to claim 11, wherein said switches areborne by said elevator and include vertically spaced actuating members,and a stationary operating member means is secured adjacent saidelevator in the path of travel of said actuating members for engagingsaid actuating members to operate said switches, said actuating membersin each group being variably spaced in accordance with a parabolicrelationship with the uppermost actuating members in said one groupbeing maximally spaced and the lowermost actuating members in said othergroup being maximally spaced.

13. Elevator apparatus according to claim 12, wherein said stationaryoperating member means comprises a pair of operating members, one forengaging the actuating members of said one group of switches and theother for engaging the actuating members of said other group ofswitches.

14. Elevator apparatus according to claim 13, wherein said elevator isadapted to stop at a plurality of vertically spaced preselected pointswhen moving upwardly and downwardly, said operating member meanscomprising a pair of said operating members for each of said points.

15. Elevator apparatus according to claim 11, wherein each of saidswitches is operable between a normal and an operated position, saidswitches being borne by said elevator and including vertically spacedactuating members, and a stationary operating member means is securedadjacent said elevator in the path of travel of said actuating membersfor engaging said actuating members to operate said switches, circuitmeans for connecting each group of switches with its associated group ofresistors, said circuit means being so arranged that when all of saidswitches are in their normal conditions, all of the associated resistorsare short circuited, and when during upward elevator movement theuppermost switch actuating member in said one group is engaged by saidoperating member means, one of said resistors from said first group isconnected across said voltage source, and as each successive actuator insaid one group is engaged by said operating member means, an additionalresistor from said one group is connected across said voltage source;said circuit means being further arranged so that when during downwardelevator movement the lowermost actuator in said other group is engagedby said operating member means one of said resistors from said othergroup is connected across said voltage source, and as each successiveactuator in said other group is engaged by said operating member meansan additional resistor from said other group is connected across saidvoltage source, and selector switch means responsive to elevatordirection for applying said voltage source to said one groups ofswitches and resistors and to said other groups of switches andresistors.

l6. Elevator apparatus according to claim 11, wherein said switches aremagnetic switches comprising contacts movable between a normal positionand an operated position, a magnet for each switch spaced from saidcontacts for biasing said contacts to their normal position; andstationary operating member means for said switches secured adjacentsaid elevator for interposition between said contacts and theirassociated magnet, said stationary operating member means being made offerromagnetic material for shielding said contacts from said magnetswhereby to cause said contacts to move to their operated positions.

l7. Elevator apparatus according to claim 1, further comprising motorcontrol circuit means including a time dependent starting program signalproducing means, means for producing a signal which is a function of thedifference between the voltage produced by said starting program meansand said proportional signal, and means for controlling the energizationof said motor in response to said last mentioned difference signal.

18. Elevator apparatus according to claim 11, further comprising motorcontrol circuit means including a time dependent starting program signalproducing means, means for producing a signal which is a function of thedifference between the voltage produced by said starting program meansand said proportional signal, and means for controlling the energizationof said motor in response to said last mentioned difference signal.

19. Elevator apparatus according to claim 17, wherein said energizationcontrolling means comprises a saturable core reactor.

20. Elevator apparatus according to claim 17, wherein said motor is amultiphase motor, and said energization controlling means comprises aplurality of saturable core reactors, one in series with each phase ofsaid motor.

1. Elevator apparatus for performing a transitionless elevator brakingprogram, said apparatus comprising: an elevator, an electric motor forpowering said elevator, a destination floor, means for producing anelectric signal proportional to the speed of said elevator,preprogrammed means for producing a signal which is a continuousfunction of the displacement of said elevator from said destinationfloor without interruption until its arrival at said destination floor,variable force brake means, and control circuit means for said brakemeans, said control circuit means including difference means forproducing a signal which is a function of the difference between thesignal produced by said preprogrammed means and said speedproportionalsignal, and means for supplying said difference signal to said brakemeans for varying the brake force in accordance with said differencesignal without interruption until the arrival and stop of said elevatorat said destination floor, whereby said transitionless elevator brakingprogram is provided until said arrival and stop.
 2. Elevator apparatusaccording to claim 1, wherein said variable force brake means includesan electromagnetic winding for reducing braking force as excitationthereof is increased, and said means for supplying said differencesignal to said brake means is continuously connected to said windinguntil the arrival of said elevator at said destination floor. 3.Elevator apparatus as in claim 2, further comprising means fordisconnecting said brake control circuit means from said winding whensaid elevator arrives at said destination floor.
 4. Elevator apparatusaccording to claim 2, further comprising switching means fordeenergizing said electric motor whenever said brake control circuitmeans is in operation.
 5. Elevator apparatus as in claim 4, furthercomprising means for maximally energizing said winding to reduce saidbrake force to a minimum whenever said electric motor is energized. 6.Elevator apparatus according to claim 2, wherein said variable brakemeans includes a brake drum and a member operatively engageabletherewith for exerting a braking torque therEon, means for biasing saidmember toward said drum to exert maximum torque thereon, saidelectromagnetic winding being in operative relation with said member forexerting a torque reducing force on said member which varies as afunction of said difference signal.
 7. Elevator apparatus according toclaim 6, wherein said biasing means comprises a spring.
 8. Elevatorapparatus according to claim 2, wherein said preprogrammed meanscomprises a voltage source, a plurality of impedances; and discreteswitching means located at spaced locations whereby to be responsive tothe distance between a preselected point on said elevator and apreselected stationary point for selectively connecting said impedancesacross said voltage source in discrete steps for varying the outputsignal produced thereby as a function of the spacing between said switchlocations and of the travel of said elevator.
 9. Elevator apparatus asin claim 8, further comprising integrating means for smoothing saiddiscrete switching transitions to provide a smooth output from saidpreprogrammed means.
 10. Elevator apparatus according to claim 8,wherein consecutive spacings between said switch locations are relatednonlinearly.
 11. Elevator apparatus according to claim 8, wherein saidswitching means comprises two groups of switches, one of said groups forupward elevator movement and the other of said groups for downwardelevator movement, and said plurality of impedances comprise two groupsof series connected resistors for connection across said voltage source,one of said resistor groups for connection during upward elevatormovement and the other of said resistor groups for connection duringdownward elevator movement, said one group of switches for selectivelyconnecting the resistors from said one group into and out of circuitacross said voltage source; and said other group of switches forselectively connecting the resistors from said other group into and outof circuit across said voltage source.
 12. Elevator apparatus accordingto claim 11, wherein said switches are borne by said elevator andinclude vertically spaced actuating members, and a stationary operatingmember means is secured adjacent said elevator in the path of travel ofsaid actuating members for engaging said actuating members to operatesaid switches, said actuating members in each group being variablyspaced in accordance with a parabolic relationship with the uppermostactuating members in said one group being maximally spaced and thelowermost actuating members in said other group being maximally spaced.13. Elevator apparatus according to claim 12, wherein said stationaryoperating member means comprises a pair of operating members, one forengaging the actuating members of said one group of switches and theother for engaging the actuating members of said other group ofswitches.
 14. Elevator apparatus according to claim 13, wherein saidelevator is adapted to stop at a plurality of vertically spacedpreselected points when moving upwardly and downwardly, said operatingmember means comprising a pair of said operating members for each ofsaid points.
 15. Elevator apparatus according to claim 11, wherein eachof said switches is operable between a normal and an operated position,said switches being borne by said elevator and including verticallyspaced actuating members, and a stationary operating member means issecured adjacent said elevator in the path of travel of said actuatingmembers for engaging said actuating members to operate said switches,circuit means for connecting each group of switches with its associatedgroup of resistors, said circuit means being so arranged that when allof said switches are in their normal conditions, all of the associatedresistors are short circuited, and when during upward elevator movementthe uppermost switch actuating member in said one group is engaged bysaid operating member means, one of said resistors from said first groupis connected across said voltage source, aNd as each successive actuatorin said one group is engaged by said operating member means, anadditional resistor from said one group is connected across said voltagesource; said circuit means being further arranged so that when duringdownward elevator movement the lowermost actuator in said other group isengaged by said operating member means one of said resistors from saidother group is connected across said voltage source, and as eachsuccessive actuator in said other group is engaged by said operatingmember means an additional resistor from said other group is connectedacross said voltage source, and selector switch means responsive toelevator direction for applying said voltage source to said one groupsof switches and resistors and to said other groups of switches andresistors.
 16. Elevator apparatus according to claim 11, wherein saidswitches are magnetic switches comprising contacts movable between anormal position and an operated position, a magnet for each switchspaced from said contacts for biasing said contacts to their normalposition; and stationary operating member means for said switchessecured adjacent said elevator for interposition between said contactsand their associated magnet, said stationary operating member meansbeing made of ferromagnetic material for shielding said contacts fromsaid magnets whereby to cause said contacts to move to their operatedpositions.
 17. Elevator apparatus according to claim 1, furthercomprising motor control circuit means including a time dependentstarting program signal producing means, means for producing a signalwhich is a function of the difference between the voltage produced bysaid starting program means and said proportional signal, and means forcontrolling the energization of said motor in response to said lastmentioned difference signal.
 18. Elevator apparatus according to claim11, further comprising motor control circuit means including a timedependent starting program signal producing means, means for producing asignal which is a function of the difference between the voltageproduced by said starting program means and said proportional signal,and means for controlling the energization of said motor in response tosaid last mentioned difference signal.
 19. Elevator apparatus accordingto claim 17, wherein said energization controlling means comprises asaturable core reactor.
 20. Elevator apparatus according to claim 17,wherein said motor is a multiphase motor, and said energizationcontrolling means comprises a plurality of saturable core reactors, onein series with each phase of said motor.